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NOAA scientists said today that a strong La Niña event, which is a periodic cooling of the tropical Pacific Ocean, helped keep the globe somewhat cooler than it would otherwise have been. La Niña tends to be associated with cooler years, but 2011 turned out to be the warmest La Niña year since records began in 1880. NOAA scientists say this is in line with global temperature trends associated with manmade global warming.

Annual records set during 2011. Credit: NOAA/NCDC.

“It’s clear over time the El Niño years tend to be the warmer years and the La Niña years tend to be the cooler years,” said Tom Karl, director of NOAA's National Climatic Data Center. “This year the La Niña-related temperatures for 2011 were as warm as anything we’ve seen in the past, very close to the year 2008.”

Every year since 1976 has been warmer than average, according to NOAA. While 2011 was the coolest year in the 21st Century, it was tied with the 2nd-warmest year of the 20th Century.

Karl said global warming has slowed, but has not paused or been reversed during the past few years, noting that the La Niña event and another Pacific Ocean cycle "tended to cool things more than might otherwise be the case” during 2011.

NASA scientists, led by James Hansen of the Goddard Institute for Space Studies in New York, said more rapid warming is likely to resume during the next few years. "We conclude that the slowdown of warming is likely to prove illusory, with more rapid warming appearing over the next few years," Hansen said.

Last year was the second wettest year over land, following the wettest year, which occurred in 2010. In the Lower 48 states, 2011 featured extraordinarily turbulent weather that wreaked havoc across the country. This stark contrast between a dry Southwest and a wet Northeast is consistent with climate change projections, Karl said. The Northeast has turned wetter since 2003, according to NOAA climate scientist Jake Crouch.

Global average temperatures during El Niño and La Niña years. Credit: NOAA/NCDC.

The U.S. experienced a barrage of extreme weather events throughout the year, with a record amount of the country experiencing either extremely dry or extremely wet conditions. Texas had its driest year on record, while seven states in the Ohio Valley and Northeast had their wettest year on record. Climate research shows that extreme precipitation events and heat waves in many parts of the world are becoming more common and more intense due in part to global warming. Also, April was the busiest month for tornadoes ever observed in the U.S., and a record six tornadoes in 2011 were rated the most intense on the scale, with EF-5 ratings.

Also Thursday, NOAA updated its list of billion dollar weather and climate events, raising it from a record-breaking 12 to 14. Additions to the list include Tropical Storm Lee, which caused widespread flooding in the Mid-Atlantic and Northeast, and a July 10-14 severe weather outbreak from the Rockies to the Midwest. The billion dollar events alone caused at least $55 billion in damage, the agency stated in a press release.